The present invention related to connectors, instrument assemblies and methods for connecting and/or disconnecting electrical connections under power. For example, the present invention relates particularly to sensor assemblies which can be connected and/or disconnected under power and to methods of connecting and/or disconnecting sensor assemblies under power. The connectors, instrument assemblies and methods of the present invention permit connection and/or disconnection under power such that the risk of igniting combustible or explosive gases in the surrounding environment is reduced and preferably eliminated.
In a hazardous environment, instruments are designed and installed in such a way that any source of ignition the instruments might produce is prevented from igniting combustible gases and/or other combustible materials in the surrounding atmosphere. For example, the device can be placed inside an explosion proof/flame proof enclosure, or the device circuitry can be made intrinsically safe. Intrinsically safe circuits are generally designed to have limited energy and are unlikely to produce an ignition source. Explosion proof/flame proof enclosures are generally designed with enough strength to withstand an internal explosion while guarding the external atmosphere from the ignition source.
When performing maintenance on an instrument installed in a hazardous environment, a user may desire to disconnect one or more assemblies or components such as a gas sensor. To perform such maintenance under current practice, the user can either declassify the area by removing all combustible or explosive gases therefrom or by removing power from the instrument to prevent the possibility of spark ignition creating an explosion or fire. Either of those choices costs the user significant time and money. Declassification or power interruption, however, may not be necessary if the instrument includes intrinsically safe circuitry which limits potential ignition energy. Although use of intrinsically safe circuitry is convenient for the user, the circuitry is more complex, costs more, and may have a power limit that does not satisfy all desired applications.
In the mining industry, the Gedcon Model 2400 Permissible Explosion-proof Connector manufactured by General Energy Development Corp. of Needham, Mass. purports to provide an explosion-proof connector for coupling two sections of multiple wire cable in which disconnection of the electrical contacts can be made with the explosion proof nature of the connector intact. That connector is also the subject of U.S. Pat. No. 4,198,110. That connector includes a receptacle housing having an insulative receptacle locked in position therein. A cooperating plug is likewise locked in position in a plug housing. An elongated dagger pin 36 in the plug housing cooperates with a receptacle in the receptacle housing to align male contact pins of the plug with the female contact sockets of the receptacle. A sleeve extends at least partially over both housings and threadingly engages with one of the housings to maintain engagement between the plug and receptacle when the sleeve is tightened. Requiring alignment of the elongated dagger pin with the cooperating receptacle to mate the contacts within the two housings of the connector during connection can be very difficult and substantially reduces the utility of that connector in an instrument assembly and elsewhere. Thus, the connector of U.S. Pat. No. 4,198,110 is generally difficult and complicated to connect properly, particularly under conditions typical of instrument assemblies installed in hazardous environment. Such instrument assemblies are often mounted on surfaces in locations which are not easily accessible.
It is desirable, therefore, to develop explosion proof connectors (for use, for example, in instrument assemblies installed in hazardous environments) and methods of connection and/or disconnection that reduce or eliminate the above-described and other problems with current connectors.
In one aspect, the present invention provides a connector or a housing for use in an environment in which a combustible material (for example, a combustible gas, a combustible dust or a combustible fiber) may be present. The connector includes a first housing section having a plurality of electrically conductive contacts therein. The connector also includes a second housing section including a plurality of electrically conductive contacts that can form an electrical connection with the contacts of the first housing section. The first housing section and the second housing section are removably connectable. The first housing section and the second housing section are capable of forming an explosion proof or flame proof (referred to collectively herein as explosion proof) housing when connected. The contacts of at least one of the second housing section and the first housing section are movable relative to their respective housing section to align the contacts of the second housing and the contacts of the first housing section during connection of the second housing section to the first housing section. Electrically conductive connection between the contacts of the first housing section and the contacts of the second housing section occurs during connection of the second housing section to the first housing section in a manner such that when connection between the contacts of the first housing section and the contacts of the second housing section occurs, the first housing section and the second housing section are in sufficient connection to form an explosion proof housing.
The contacts of the first housing section can, for example, be in electrical connection with a first cable (for example, a multiple-wire connector) and the contacts of the second housing section can, for example, be in electrical connection with a second cable.
Moreover, the connector of the present invention can also form an instrument housing wherein one of the first housing section and the second housing section includes at least one instrument component in electrical connection with the contacts of that housing. At least one of the contacts of the other of the first housing section and the second housing section is adapted to transmit electrical power to the instrument component when the first housing section and the second housing section are connected.
In another aspect, the present invention provides a method of forming a connection between electrically conductive contacts in an environment in which a combustible material may be present, including the steps of:
(a) connecting a second housing section, including a plurality of electrically conductive contacts that can form an electrical connection with a plurality of electrically conductive contacts of a first housing section, to the first housing section;
(b) permitting at least one of the plurality of contacts of the second housing section and the plurality of contacts of the first housing section to move relative to their respective housing section to align the contacts of the second housing and the contacts of the first housing section during connection of the second housing section to the first housing section, and
(c) making electrically conductive connection between the contacts of the second housing section and the contacts of the first housing section during connection of the second housing section to the first housing section in a manner such that when connection between the contacts of the first housing section and the contacts of second housing section occurs, the first housing section and the second housing section are in sufficient connection to form an explosion proof housing.
In still a further aspect, the present invention provides a gas sensor assembly for use in an environment in which a combustible material may be present including a first housing section having a plurality of electrically conductive contacts therein. At least one of the contacts of the first housing section is electrically connectible to a power source. The contacts of the first housing section can, for example, be seated in a slotted, protective cover to prevent inadvertent contact with other conductive devices when the first housing section and a second housing section are disconnected.
The gas sensor assembly also includes a second housing section preferableyhaving a plurality of electrically conductive contacts that can form an electrical connection with the contacts of the first housing section. At least one of the contacts of the second housing section is in electrical contact with a gas sensor. The first housing section and the second housing section are removably connectable and are capable of forming an explosion proof housing when connected. The contacts of at least one of the second housing section and the first housing section are movable relative to their respective housing section to align the contacts of the second housing and the contacts of the first housing section during connection of the second housing section to the first housing section. As described above, electrically conductive connection between the contacts of the first housing section and the contacts of the second housing section occurs during connection of the second housing section to the first housing section in a manner such that when connection between the contacts of the first housing section and the contacts of second housing section occurs, the first housing section and the second housing section are in sufficient connection to form an explosion proof housing.
Preferably, electrical connection between the contacts of the first housing section and the contacts of the second housing section is broken during disconnection of the second housing section from the first housing section in a manner such that when disconnection between the contacts of the first housing section and the contacts of second housing section occurs, the first housing section and the second housing section remain in sufficient connection to form an explosion proof housing.
In one embodiment, the second housing section is moved axially away from the first housing section during disconnection and the second housing section is moved axially toward the first housing section during connection. The second housing section can, for example, include threading that cooperates with threading on the first housing section so that rotating the second housing section relative to the first housing section causes relative axial movement between the second housing section and the first housing section. In one embodiment, the second housing section includes a seating member to which the contacts of the second housing are attached. The seating member is rotatably attached to the second housing member. The seating member includes an abutment member that abuts an abutment member of the first housing section to prevent rotation of the seating member of the first housing section relative to the second housing section when the contacts of the second housing section are in a predetermined alignment with the contacts of the first housing section during connection of the second housing section to the first housing section.
The instrument assemblies and methods of the present invention eliminate the need to declassify an area or the need to interrupt or disconnect power to an instrument during connection and/or disconnection of certain housing sections and associated internal electrical contacts thereof by extending the use of an explosion proof enclosure. Because electrical contact of one or more components within the instrument are connected and/or disconnected while the integrity of the explosion proof enclosure remains intact, any spark thereby created cannot ignite any combustible gases in the external atmosphere. For example, a sensor or other component can be removed for replacement or repair without risk of ignition. Once the housing sections of the instrument are disconnected and the sensor or other internal components are removed, the electrical contact(s) that remain under power are preferably protected from damage or short circuit by a protective, insulating or nonconductive cover, or by being recessed. Replacement of a sensor or other instrument assembly and reconnection of the housing sections of the instrument are accomplished in a similar manner.
Preferably, as the sensor or other internal component is replaced and the housing sections of the instrument are reconnected, contacts associated with the housing sections are automatically aligned regardless, for example, of the relative rotational alignment of the housing sections at the beginning of connection, to prevent improper mating or connections. Polarization or unique alignment of one or more of the contacts can be used for additional assurance that proper alignment is achieved. The self-alignment of the contacts of the housing sections during connection thereof facilitates assembly of the connectors of the present invention. Indeed, such connectors are well suited for use in hazardous environments by industrial workers who may be wearing personal protective equipment.
In general, as a sensor or other instrument assembly of an instrument of the present invention is installed, the explosion proof properties of the enclosure are achieved first, then connection between the electrical contacts is made so that any potential ignition sources are contained within the explosion proof enclosure. As a result, intrinsically safe circuitry and any associated power limitations are not necessary. Moreover, power interruption to the instrument is not required, thereby saving the end user time and money while providing more options than currently are available.
The present invention, along with the attributes and attendant advantages thereof, will best be appreciated and understood in view of the following detailed description taken in conjunction with the accompanying drawings.